Chapter 19 - genetics of living systems Flashcards
(13 cards)
State the four key parts of an operon (4)
Structural genes, promoter, operator, regulatory gene (4)
describe the process of transcription in detail (4)
DNA helicase attaches to DNA andhydrogen bonds betweenbases are broken. (1) FreeRNA nucleotidespair with the exposed, complementary DNA nucleotides of the template strand. (1) Phosphodiesterbonds formbetween the RNA nucleotides due to RNA polymerase (1). This produces mRNA which can then leave the nuclear pore (1).
define chromatin (2)
DNA (1) wound around histones (proteins) (1)
Define epigenetics (2)
Influencing gene expression (1) without changing the genome (1)
Describe what happens during methylation of histones (3)
Methylation groups make the histones more hydrophobic so they tightly bind to each other. (1) Prevents transcription of mRNA, by stopping RNA polymerase binding (1) mRNA not transcribed so gene repressed (‘switched off’) (1)
Describe what happens during acetylation of histones (3)
Acetylation reduces positive charge on histones (1) DNA less tightly packed (1) Genes can be transcribed (“switched on”) (1)
How does euchromatin differ from heterochromatin? (2)
Euchromatin = loosened chromatin (1) Heterochromatin = restricted chromatin (1)
Explain the action of an ‘activator’ (a type of transcription factor) (3)
An activator (transcription factor) binds to promoter region on DNA (1). This causes RNA polymerase to bind to the promoter region (1). RNA polymerase will then start transcription and gene is expressed (1)
Explain the action of an ‘repressor’ (a type of transcription factor) (3)
A repressor (transcription factor) (1) binds to operator region on DNA (1). This blocks RNA polymerase (1) and represses transcription and the gene is not expressed (1)
what is an operon (2)
A sequence of DNA containing a cluster of genes (1) under the control of the same regulatory mechanism (1).
what specifically is the lac operon (1)
An operon required for the metabolism of lactose in bacteria (1)
Which genes are in this operon? What do they code for?
What is the role of :The regulatory gene, structural genes, promoter, operator
Describe what is happening when no lactose is present
Describe what is happening when there is lactose present
What other molecules help speed up the transcription process? (not shown on diagram)
LacZ, lacY and lacA. Genes that code for enzymes that breakdown lactose (lactase)
Regulatory gene – produces a small protein molecule called a repressor
Structural genes – genes that are collectively regulated by the operon
Promoter – upstream sequence to which RNA polymerase binds
Operator – segment of DNA to which a repressor protein binds (inhibits transcription by obstructing RNA polymerase)
A regulatory gene is located near to the operon and codes for a repressor protein that prevents transcription of lacZ, lacY and lacA if there is no lactose. RNA polymerase therefore cannot bind to the promoter and transcription does not occur.
If lactose is present, it binds to the repressor protein causing it to change shape so it can no longer bind to the operator. As a result RNA polymerase can bind to promoter and regulate the genes and the enzymes are synthesised!
CRP (cAMP receptor protein) binding to the operon increases the rate of transcription. This is only possible if CRP is bound to cAMP
What is the purpose of the regulatory gene? (1)
Where do transcription factors (activators) bind to? (1)
Where do repressors bind to? (1)
State what happens to CRP and cAMP if there is low levels of glucose at the lac operon (3)
Describe the process of alternative splicing (2)
What is the purpose of the adenine chain being added to primary mRNA? (2)
Describe an example of post-translational control of gene expression (4)
Produces a repressor protein
Promoter
Operator
cAMP increases if glucose is low (1) and binds to CRP (1). This causes CRP to bind to the lac operon, increasing the speed of transcription (1)
Removal of exons (1) to give a range of different polypeptide chains from 1 gene (1)
Stabilise the mRNA (1) and facilitate its exit from the nucleus (1)
Some proteins are not functional straight after they have been synthesised. Protein activation is controlled by molecules such as hormones (1). These molecules bind to receptors on the cell membrane of the cell (1) which causes ATP to be converted cAMP (second messenger) (1). cAMP then activates proteins by altering their 3D structure (1).
